Cortisol Detection in Undiluted Human Serum Using a Sensitive Electrochemical Structure-Switching Aptamer over an Antifouling Nanocomposite Layer

Abstract

There is a strong and growing need to monitor stress biomarkers in vivo for real-time emotional and wellness assessment. Toward this, we report a reagent-free electrochemical aptasensor with a nanocomposite antifouling layer for sensitive and continuous detection of cortisol in human serum. A thiolated, methylene blue (MB)tagged conformation-switching aptamer was immobilized over a gold nanowire (AuNW) nanocomposite to capture cortisol and generate a signal proportional to the cortisol concentration. The signal is recorded through differential pulse voltammetry (DPV) and chronoamperometry. The aptasensor exhibited a sensitive response with 0.51 and 0.68 nM detection limits in spiked buffer and undiluted serum samples, respectively. Interference from other structurally similar analogs, namely, epinephrine and cholic acid, was negligible (<10%). The developed nanocomposite-based aptasensor showed excellent stability in undiluted human serum, outperforming several other nanocomposite materials even after prolonged exposure. This work lays the foundation for new biosensor formats such as implantable and wearable sensors.

Electrochemical Carbamazepine Aptasensor for Therapeutic Drug Monitoring at the Point of Care

“…Statistical analysis was performed using Origin 9.0. The limit of detection (LOD) was calculated using the slope method, where LOD = 3 × SD of the blank/slope …”

“…The limit of detection (LOD) was calculated using the slope method, where LOD = 3 × SD of the blank/slope. 35 …”

“…This work uses an aptamer as an affinity reagent to overcome the prior work’s lack of specificity and high oxidation potential. Aptamers are artificial oligonucleotides selected in vitro and possess a high binding affinity to their target, ranging from small molecules to cells. − Aptamers can be used in various applications (e.g., medical biology, microbiology, medicine, analytical chemistry, etc.) due to their high specificity and selectivity. − Compared to antibodies, the gold standard in affinity assays, aptamers have several unique properties (i.e., temperature stability, in vitro synthesis, ease of chemical modification, longer shelf life, etc.)…”

“…Aptamers are artificial oligonucleotides selected in vitro and possess a high binding affinity to their target, ranging from small molecules to cells. 33 − 35 Aptamers can be used in various applications (e.g., medical biology, microbiology, medicine, analytical chemistry, etc.) due to their high specificity and selectivity.…”

Nanomaterials for Cortisol Sensing

“…Singh and co-workers developed a reagent-free electrochemical aptasensor with a nanocomposite antifouling layer to monitor in vivo stress biomarkers such as cortisol [ 76 ]. This electrochemical sensor is based on a conformation-switching aptamer, on top of a conductive antifouling nanocomposite surface, to detect cortisol in undiluted human serum, as shown in Figure 16 .…”